Dual technology sensors in the security field combine passive infrared (PIR) sensors and microwave Doppler motion detectors to increase the reliability of detecting an intruder. A PIR sensor typically has a 90-degree detection pattern, allowing it to detect motion 45 degrees to the left of center and 45 degrees to the right of center, while a microwave detector typically has a detection pattern greater than 90 degrees (for example, 160 degrees), allowing it to detect motion at a much wider angle to the left and right of center. (In the example 80 degrees to the left of center and 80 degrees to the right of center). In order to provide complete coverage of a protected area by the PIR sensor, the dual technology sensor is typically mounted in a corner of the protected area. In this configuration the PIR sensor's detection pattern substantially matches the protected area, while the microwave detector's detection pattern is larger than the protected area and allows a moving object outside the protected area to be detected by the microwave detector. This may compromise the reliability of the dual-technology sensor. It is desirable to distinguish detected motion by the microwave detector that is outside the protected space from detected motion within the protected space, thereby limiting the microwave detector's field of view to the protected space and generate an alarm only when the detected motion is within the protected space. It is also desirable to generate a warning (not an alarm) when motion is detected outside the protected space and moving toward the protected space.
In a different situation, such as in a museum, it may be useful to be able to change the size of the microwave detector's field of view at selected times. For instance, when the museum is closed, the microwave detector covers the entire protected space while the PIR sensor only covers the area near an exhibit using a narrow beam lens. If the microwave detector detects motion inside the protected area that is going toward the exhibit, the sensor will generate a warning. If both the PIR sensor and the microwave detector detect motion, an alarm will be generated. However, when the museum is open, rather than covering the entire protected space, motion detection may only be required near an exhibit. This allows protection of the exhibit from being stolen or defaced and allows visitors to view the exhibit. Therefore, the visitor's motion should only set off an alarm when the visitor is too close to an exhibit. A single dual technology sensor that has a microwave detector with a variable field of view in accordance with this invention can provide intrusion detection for both of these situations. When the museum is closed, the field of view of the microwave detector is selected to equal the entire protected space. When the museum is open, however, the field of view of the microwave detector is narrowed to a smaller region that equals that of the PIR sensor.
Having the ability to select the microwave detector's field of view allows a dual technology sensor to be adapted to very specific situations. Another example of this is a long corridor/aisle, which can be protected by changing the lens for the PIR sensor and narrowing the microwave detector's field of view to match that of the PIR sensor.
It is an object of the present invention to distinguish between motion detected by a microwave detector that is outside a defined protected space and motion detected by a microwave detector that is inside the defined protected space.
It is a further object of the present invention to match the field of view of the microwave detector with the detection pattern of the PIR sensor.
It is a further object of the present invention to limit the field of view of the microwave detector to be narrower than the detection pattern of the PIR sensor.
It is a further object of the present invention to be able to select the microwave detector's field of view based on a condition, such as the time of day.
Finally, it is a further object of the present invention to generate a warning when the microwave detector detects motion that is outside the protected space and is moving toward the protected space.